A wide variety of fuel systems are well known and widely used in modern internal combustion engines. Fuel may be pressurized for injection and stored in a so-called common rail that serves as a reservoir of pressurized fuel for delivery to individual fuel injectors, typically in fluid communication directly with combustion cylinders in the engine. In other designs mechanical unit injectors each include a cam-actuated plunger that pressurizes fuel for injection by one of a plurality of fuel injectors in the engine, or in some instances each plunger charges a pressure accumulator that stores pressurized fuel for less than all of the fuel injectors in the engine. Both types of systems have certain advantages and disadvantages.
In the case of mechanically actuated unit injectors the fuel system, and in particular the valvetrain, can be a significant source of undesirable engine noise. Depending upon jurisdictional requirements, engine type, operating strategies, and variations engine to engine, noise produced by the engine can range from a relatively minor annoyance to an operating property that has to be managed. Specialized parts in the nature of ground gears, viscous dampers, and expensive noise panels can be required to reduce engine noise to acceptable levels. The use of such noise management equipment can add not only expense but also complexity, weight, packaging issues and other undesired properties to the engine.
U.S. Pat. No. 6,595,189 to Coldren et al. is directed to a method of reducing noise in a mechanically actuated fuel injection system. The strategy proposed by Coldren et al. employs a flow restriction between a fuel pressurization chamber of the fuel injector and a fuel source, ostensibly for the purpose of limiting momentum of fuel exiting the fuel injector past a spill valve. Where such exiting fuel has sufficient momentum it can produce physical separation followed by rapid reengagement of cooperating engine components. Coldren et al. indicates sufficient contact force can be maintained between the various engine components to reduce the mechanical noise levels. The strategy set forth in Coldren et al. appears to have applications for certain sources of excessive engine noise, however, there is always room for improvement and advancements in this field.